1. Technical Field
The present invention relates to a paper sheet humidifying device to straighten paper sheets by applying water to the paper sheets to remove curvatures, undulations, waves and the like; a paper sheet post-processing apparatus built-in with the paper sheet humidifying device; and an image forming system built-in with the paper sheet humidifying device.
2. Background Technology
As a paper sheet post-processing apparatus of an electrophotographic image forming apparatus, a paper sheet humidifying device for humidifying the paper is utilized.
Among various types of the proposed paper sheet humidifying devices, a paper sheet humidifying device provided with a pair of humidifying rollers for applying water to the paper sheet and water supply rollers for supplying water to the pair of humidifying rollers is disclosed in Japanese Patent Application Publication No. 2006-8282 (Patent document 1) and in Japanese Patent Application Publication No. 2008-94585 (Patent document 2).
In the paper sheet humidifying device of Patent document 1, a water supply roller continuously supplies water to the pair of humidifying rollers, and the humidifying rollers continuously humidify the paper sheet being conveyed.
The water supply roller in the Patent document 1 is dipped in the water contained in a container, and continuously scoops up the water by being rotated.
In the paper sheet humidifying device of Patent document 2, a pair of water supply rollers respectively contact the pair of humidifying rollers, and supply the water to the humidifying rollers.
The pair of water supply rollers in the Patent document 2 is dipped in the water contained in a water supply plate, and continuously scoops up the water by being rotated.
According to the Patent document 2, the water in the water supply plate is continuously supplied from a water feed pipe, and a level of the water in the water supply plate is kept in a prescribed level by overflowing.
In the paper sheet humidifying device described in the Patent document 1, the water level in a container is kept constant by the control of water supply system for supplying water to the container. In the case of Patent document 1, accuracy of water supply system for supplying water to the surface of water supply roller, in other words the accuracy of keeping the water level in the container, further, the accuracy of homogeneity of humidifying the paper sheet depend on accuracy of supplying water onto the water supply roller. Therefore in cases where the water supply system does not work correctly, the water level in the container varies, and consequently homogeneous humidification may not be performed due to the variation of humidifying amount of the paper sheet.
Further, foreign substances mixed into the water in the container increase as the humidification continues. The increased foreign substances are transferred to the water supply roller and further to the humidifying roller to cause uneven humidification or attachment the paper sheet with foreign substances.
According to the Patent document 2, the water level in the water supply plate is maintained constant by overflowing of the water, and the water level is kept constant with a high degree of accuracy.
Further, the water removed of foreign substances is always supplied to the water supply plate, and the water to be supplied is constantly replaced with the new one due to the overflowing. Thus, the problem of mixing-in with the foreign substances is prevented.
In this way, the paper sheet humidifying device of Patent document 2 is improved in some aspects compared to that of Patent document 1. However, it is revealed in the humidifying device of Patent document 2 that the water possibly flows out from a drain tank which accepts the water overflowed from the water supply plate.
In the paper sheet humidifying device of Patent document 2, the water in the drain tank is ejected through a drain pile to a water storage tank, thus during a proper movement the water never accumulates in the drain tank. However, in cases where the drain pipe clogs up with fragments of the paper sheet and the like, the water may flow out from the drain tank.
This type of problem never occurred in the paper sheet humidifying device of Patent document 1, since a water supply control is conducted to keep the water level in the container constant, and the water supply is stopped when the water level rises over a prescribed level. Therefore, the water level never exceeds the prescribed level, and the water is never caused overflowing.